AC/DC converters, such as those used to charge and/or power electronic devices such as desktop computers, notebook computers, tablet computers, smartphones, and the like, may be required to work at a wide range of input voltages. For example, nominal input voltage in the US might be 120 VAC, while nominal input voltages in Europe and other regions might be 240 VAC. Thus, when accounting for safety margins, an operating range of 90 VAC to 265 VAC might be required. Traditionally, such converters produced a single output voltage, but the advent of the USB-PD (Universal Serial Bus Power Delivery) standard has introduced multiple output voltages as a requirement in some cases. In some embodiments, it might be desired to provide output voltages of around 5V for devices such as phones up to 20V or more for laptops. The wide range of input and output voltages has introduced a number of challenges into the design of such converters.
Traditionally, the flyback topology has been used for such converters, largely due to its design flexibility. However, the flyback topology often introduces other design issues, such as switching noise, high voltage rating requirements for components, parasitic capacitances associated with shielding requirements, large component values (e.g., bulk capacitors), etc., as well as increased losses associated with efficiency limitations inherent to existing flyback topologies. Additionally, as power requirements increase, power factor correction or other input current conditioning may be required to meet regulatory requirements. Historically, this has often led to two stage designs, which increase cost, reduce efficiency, and increase complexity of both the circuit and controller design.
Thus, what is needed in the art is a single stage converter design that can accommodate wide ranges of input and output voltages, while providing for increased efficiency, improved noise performance, reduced component values and ratings, and suitable input power conditioning.